The present invention relates to a display-screen-sharing system for allowing a display screen to be shared among a plurality of terminals, a display-screen-sharing method adopted by the system, transmission side and reception-side terminals used in both the system and the method, and a recording medium.
A display-screen-sharing system has been proposed as a conventional system in which a network is used for connecting a plurality of terminals remote from each other as terminals to be used in a data conference. The proposed display-screen-sharing system is capable of allowing a display screen shown on a terminal used by a presenter to be shared by terminals used by other participants of the data conference. In this display-screen-sharing system, the terminal used by a presenter (transmission-side terminal) transmits data of the display screen to terminals used by other participants (reception-side terminal) and the terminals used by other participants each reproduce the data on a display screen so that each of the other participants is capable of browsing information such as the contents of a presentation given by the presenter and the contents of a displayed material.
In the conventional display-screen-sharing system, data of a display screen on the transmission side is generally encoded at a proper frame rate according to network parameters such as a transmission rate assumed in advance in the same way as, for example, transmission of a moving picture by adoption of a streaming technique, and results of encoding are transmitted to reception sides at predetermined time intervals. In addition, every time the display screen is updated on the transmission side, the data of the updated display screen is transmitted sequentially one piece after another to the reception side without regard to the processing state on the reception side.
In the method adopted by the conventional display-screen-sharing system as a method of transmitting data of a display screen, however, not only does the load borne by the transmission-side terminal inevitably increase, but unnecessary data generated in a picture-rendering process carried out in a reception-side terminal is also transmitted, raising a problem of an unavoidably increased amount of the network traffic. Particularly, in a data conference or the like, there are many cases in which it is sufficient to transmit the contents of a presentation or the like as data of still pictures. In such cases where still pictures required after a picture-rendering process are demanded more than moving pictures are necessary in the course of the picture-rendering process so that complete real-time conditions are not needed between the transmission and reception sides, the conventional transmission technique described above results in much waste in data transmission, making the transmission inefficient.
In addition, since data of a display screen is transmitted continuously on a one-sided basis without regard to the processing state on the reception side, there is raised a problem that it is quite within the bounds of possibility that a reception-side terminal bears an excessively heavy load and/or an overflow occurs in a buffer employed in the reception-side terminal.